The variable above is marked as obsolete but used in font-core.el. Should
it be that way?
Obviously even obsolete variables have to be used _somewhere_, else
they are not just obsolete but totally useless. Can you elaborate on
your question?
The variable is marked obsolete in the same file where it is used.
I would expect that the new name where used in that file instead of
the old.
To clear the misunderstanding, let me put it differently:
font-lock-defaults-alist is still *obeyed* by the current code (which is
why it's "obsolete" and not "removed"), but it is not *used* by the
current code.